The dioxazine pigment class is well known for its strong bluish-red to violet colors. Due to its outstanding tinctorial strength and saturation and excellent heat and light resistance, carbazole dioxazine, C.I. Pigment Violet 23, became the most important dioxazine violet on the worldwide pigment market. In general, C.I. Pigment Violet 23 has a violet color, a particle size less than 0.5 .mu.m and a specific surface area greater than about 25 m.sup.2 /g.
In general, carbazole dioxazine crude has a greenish color, a particle size greater than 0.5 .mu.m and a specific surface area from about 2 to 20 m.sup.2 /g and can be processed into C.I. Pigment Violet 23. Carbazole dioxazine crude can be prepared according to the process disclosed in JP 56141355 A2 (Chem. Abstr., 96(1):70437d).
It is known in the art to process carbazole dioxazine crude into C.I. Pigment Violet 23 by reducing its particle size. U.S. Pat. No. 4,785,999 describes the dry milling of polycyclic crude pigments. The German patent, DE 2,742,575 describes the dry grinding of large crystals of unrefined carbazole dioxazine crude in an oscillating mill, followed by treatment of the milled materials with solvents containing surfactants and weak acids to produce C.I. Pigment Violet 23. In EP 075,182, the carbazole dioxazine crude is treated with polyphosphoric acid followed by drowning into water, ice and/or a water miscible organic liquid to produce C.I. Pigment Violet 23. U.S. Pat. No. 4,804,417 discloses pigment-grade dioxazine violet produced from crude material by converting to the sulphate followed by hydrolysis and treatment with alcohol and inorganic salt. The processed pigment has a cleaner hue, greater color strength, good dispersibility, smaller particle size (less than 0.5 .mu.m) than the crude material and a specific surface area over 25 m.sup.2 /g.
Prior to the present invention, it was believed in the art that the carbazole dioxazine crude had little coloring value on its own and was useful only as an intermediate for the production of C.I. Pigment Violet 23. The present process utilizes carbazole dioxazine crude directly as a pigment in order to generate unique color effects, without processing the carbazole dioxazine crude into C.I. Pigment Violet 23. Thus, the present invention relates to the discovery of a new utility for carbazole dioxazine crude; its use as a pigment to produce new color effects.